Commercial video production typically involves acquiring and editing video sequences. Before being distributed, colors in the video production may be adjusted in a color grading step. Color grading typically involves displaying the video production on a reference display under ideal viewing conditions and adjusting colors and tones in the video production to achieve a desired artistic intent. For example, a person operating color grading apparatus (a ‘color grader’) may decide to make the mood of a scene gloomy by reducing the brightness of the image. Artistic goals may also be met by making other adjustments, for example, changing the colors of certain displayed objects, changing the overall contrast in the scene, changing the overall brightness of the scene, and the like. The result, when displayed on the reference display, matches the artistic intent of the color grader.
A wide number of alternative display technologies are available commercially. These range from digital cinema displays to television sets which may be based on cathode ray tubes, plasma displays, LED displays, LCD panel displays in which the LCD panel is backlit by various types of backlight systems, and the like. Different displays have different capabilities. For example, some displays may have a broader color gamut than other displays. Some displays may be capable of reproducing a broader range of brightnesses and/or a higher maximum brightness than other displays. The inventors have recognized a need for methods and apparatus capable of transforming image data in a manner which can take advantage of the capabilities of a particular display without compromising the artistic intent represented by the images in the image data.
This need also extends to reproductions of still images by various types of printing, engraving, and other image reproduction technology in which the reproduction technology may have capabilities for reproducing colors and/or tones that are different from those assumed by the image data.
There remains a need for flexible and cost-effective tone and/or gamut mapping apparatus and methods. There is a particular need for such apparatus and methods that may be applied to produce enjoyable images on high quality displays.